As a new rapid prototyping (RP) technology, solid freeform fabrication (SFF) or layer manufacturing involves building a three-dimensional (3-D) object layer by layer or point by point. A SFF system quickly produces models and prototype parts from 3-D computer-aided design (CAD) geometry data, computed tomography (CT) scan data, magnetic resonance imaging (MRI) scan data, and model data created from 3-D object digitizing devices. A SFF system joins liquid, powder, and sheet materials point-by-point or layer-by-layer to form physical objects.
A typical SFF process normally begins with creating a Computer Aided Design (CAD) file to represent the geometry of a desired object using solid modeling software. In one commonly used approach, this CAD file is converted to a stereo lithography (.STL) format in which the exterior and interior surfaces of the object is approximated by a large number of triangular facets that are connected vertex-to-vertex. A triangular facet is represented by three vertex points each having three coordinates: (x.sub.1,y.sub.1,z.sub.1), (x.sub.2,y.sub.2,z.sub.2), and (x.sub.3,y.sub.3,z.sub.3). A perpendicular unit vector (i,j,k) is also attached to each triangular facet to represent its normal for helping to differentiate between an exterior and an interior surface. This object geometry file is further sliced into a large number of thin layers with each layer being composed of a plurality of segments defined by many polygons. The layer data are converted to tool path data in terms of computer numerical control (CNC) codes or other similar machine control codes. These codes are then utilized to drive a fabrication tool for building an object point by point and/or layer by layer.
SFF technologies have been used to produce prototypes of injection-molded parts and metal castings that go into everything from mobile phones, computers, and copy machines to car instrument panels, aircraft subassemblies, and medical diagnostic instruments. SFF technologies may also be used in rapid tooling (RT). For instance, SFF-generated patterns are used to produce molds. Core and mold inserts can be produced directly from a digital database layer by layer. Use of SFF could reduce tool-making time and cost, and provide the opportunity to modify mold or die design without incurring high costs and lengthy time delays. SFF also has potential as a cost-effective production process if the number of parts needed at a given time is relatively small. Further, it can be used to fabricate certain parts with a complex geometry which otherwise could not be made by traditional fabrication approaches. SFF technologies produce freeform solid objects directly from a digital model without part-specific tooling or human intervention. The SFF-based RP technology has enjoyed a broad array of applications such as verifying CAD database, evaluating design feasibility, testing part functionality, assessing aesthetics, checking ergonomics of design, aiding in tool and fixture design, creating conceptual models and sales/marketing tools, generating patterns for investment casting, and reducing or eliminating engineering changes in production.
While in some of these applications, such as the verification of CAD design and testing of part functionality, the formation of a colorful object may not be essential, in other applications, such as aesthetics assessment, it may be desirable to have different colors on different parts of an object. Color is appreciated to be a strong communicator and no major mainstream media can function without it. A colorful prototype model can tell volumes about the nature of a design. There is a world of difference when it comes to the comparison between a color TV and a black-and-white TV, or between a color photo and a black-and-white photo. This notion suggests that a colorful prototype will convey much more to a viewer as compared to a single-color model.
Generally speaking, however, automated SFF techniques that are currently available for building 3-D parts do not provide adequate color manipulating capabilities. One commercially available system commonly referred to as stereo lithography (Sly), for instance, employs software to slice a computer generated solid model, represented by CAD data, into thin cross sections. The cross sections are then physically created by scanning a spot of ultraviolet laser light over the top surface of a reservoir of photo-curable liquid polymer. The scanned laser spot partially cures the polymer, changing it from a liquid to a solid. After forming a given layer an object platform that supports this first layer is lowered within the reservoir by an amount equal to the thickness of the layer created. A new layer of fresh polymer is re-coated over the previous layer and the scanning/curing process is repeated. These procedures are repeated for the next layers until the object is completed. After fabrication subsequent steps are required to drain the unused resin and to fully cure all of the photo polymer that may be trapped within the partially cured material. The SLy systems make use of single-color photo-curable polymers to make an object; each reservoir containing one type of single-color resin at a time. These systems do not provide the capability for the operator to vary the color of an object during the build process.
In another type of commercially available system, selective laser sintering (SLS), a thin layer of heat-fusible powder is spread over a surface by a counter rotating cylinder. A laser is employed to scan the powder layer, while its beam is modulated to melt the powder only in areas defined by the geometry of the cross section. A new layer of powder is then spread and melted, and the process is continually repeated until the part is completed. In each current SLS system, only one powder-feeding cylinder is permitted to operate during an object-building process even though, in principle, different cylinders may be used alternatively to feed powders of different colors for different layers. Even with several powder-feeding cylinders being available for one SLS system, however, this process is not capable of generating an object with different colors at different locations of a layer (unless, of course, the cylinders are able to feed different color powders to different spots of a layer; but, this is not presently possible).
Another commercially available system, fused deposition modeling (FDM), employs a heated nozzle to extrude a melted material such as nylon wire or wax. The starting material is in the form of a rod or filament that is driven to move like a piston. The front end, near the nozzle tip, of this piston is heated to become melted; the rear end or solid portion of this piston pushes the melted portion forward to exit through the nozzle tip. The nozzle is translated under the control of a computer system in accordance with previously sliced CAD data. The FDM technique was first disclosed in U.S. Pat. No. 5,121,329 (1992), entitled "Apparatus and Method for Creating Three-Dimensional Objects" issued to S. S. Crump. A most recent patent (U.S. Pat. No. 5,738,817, April 1998, to Danforth, et al.) reveals a fused deposition process for forming 3-D solid objects from a mixture of a particulate composition dispersed in a binder. The binder is later burned off with the remaining particulate composition densified by re-impregnation or high-temperature sintering. Commercially available FDM machines, each one being capable of feeding two types of filaments (one for the part being built and the other for the support structure), are not equipped for providing predetermined color pattern variations. Batchelder, et al. (U.S. Pat. No. 5,402,351, 1995 and U.S. Pat. No. 5,303,141, 1994) reveal a model generation system having closed-loop extrusion nozzle positioning. These melt extrusion based deposition systems provide only a fixed-composition feed and do not lend themselves to varying the color of an object.
It may be noted that all the SFF processes cited so far are related to making an object by depositing (adding) material to build individual layers (instead of removing un-wanted material from an otherwise full layer) and, hence, are commonly referred to as "layer-additive" processes.
In a series of U.S. patents (U.S. Pat. No. 5,204,055, April 1993, U.S. Pat. No. 5,340,656, August 1994, U.S. Pat. No. 5,387,380, February 1995, and U.S. Pat. No. 5,490,882, February 1996), Sachs, et al. disclose a 3-D printing technique that involves using an ink jet to spray a computer-defined pattern of liquid binder onto a layer of powder. The binder serves to bond together those powder particles on those areas defined by this pattern. Those powder particles in the un-wanted regions remain loose or separated from one another and will be removed at the end of the build process. Another layer of powder is spread over the preceding one, and the process is repeated. The "green" part made up of those bonded powder particles is separated from the loose powder when the process is completed. This procedure is followed by binder removal and metal melt impregnation or sintering. This process, as currently practiced, involves spraying single-color powder particles and single-color liquid binder to build all layers of an object and, therefore, does not provide an ability to build variable multi-color object.
In another series of U.S. Patents (U.S. Pat. No. 4,752,352, June 1998, U.S. Pat. No. 5,354,414, October 1994, U.S. Pat. No. 5,637,175, June 1997), Feygin reports a technique called laminated object manufacturing (LOM). In this technique, a material delivered in a thin sheet form, coated with thermally activated adhesive, is glued to the previous layer by use of a heated roller. A laser outlines a CAD-defined cross section onto the sheet and, in non-solid (unwanted) areas of the layer, it scribes a cross-hatch pattern of small squares. As the procedures repeat, the cross-hatches build up into "tiles" which are broken off the solid block and later removed to yield a finished part. This process represents a "layer-subtractive" process because each layer begins with supplying a full layer of sheet-like material and removing or subtracting the un-wanted portions of the layer. In the LOM methods currently being practiced, a continuous roll of paper of a uniform color (same color everywhere on the paper) is operated to build an object of single color. With the current LOM machines in operation, it would be difficult to alternately feed layers of different colors on demand and would be impossible to vary colors for different spots of a layer.
In U.S. Pat. No. 5,015,312, issued May 14, 1991, Kinzie discloses a method and apparatus for constructing a 3-D surface of predetermined shape and color from a length of sheet material. This method begins by making a series of color profiles along one side (not edge) of the sheet material in sequence. Each color profile corresponds in shape and color to the shape and color of a different cross section of the surface to be constructed. Areas on the sheet material outside of the profiles are then removed and discarded so as to leave a series of unconnected planar elements. Each planar element has an edge shape or outline corresponding to a crosssection of the surface with the color profile itself forming at least a color border or margin on the surface of its respective planar element around the edge. These individual planar elements are then glued together in a proper sequence to form a "laminated" structure. When viewed, the entire surface of this structure appears to be colored even though the color is applied only along one side (top or bottom surface, but not along the edges) of individual planar elements. This method does provide a variable multi-color exterior surface of an object. This layer-subtractive method, however, pays little attention to the formation of interior features (e.g., shape and dimension of a channel) of a 3-D object. A useful prototype requires the formation of more than just its outside surface. Further, the final stacking-up and lamination procedures must be carried out manually and the creation of color profiles on each layer is a lengthy procedure. Hence, this process is expected to be slow and labor intensive.
In U.S. Pat. No. 5,514,232, issued May 7, 1996 and U.S. Pat. No. 5,879,489, issued Mar. 9, 1999, Burns discloses a method and apparatus for automatic fabrication of a 3-D object from individual layers of fabrication material having a predetermined configuration. Each layer of fabrication material is first deposited on a carrier substrate in a deposition station. The fabrication material along with the substrate are then transferred to a stacker station. At this stacker station the individual layers are stacked together, with successive layers being affixed to each other and the substrate being removed after affixation. One advantage of this method is that the deposition station may permit deposition of layers with variable colors or material compositions. In real practice, however, transferring a delicate, not fully consolidated layer from one station to another would tend to shift the layer position and distort the layer shape. The removal of individual layers from their substrate also tends to inflict changes in layer shape and position with respect to a previous layer, leading to inaccuracy in the resulting part.
In U.S. Pat. No. 5,301,863 issued on Apr. 12, 1994, Prinz and Weiss disclose a Shape Deposition Manufacturing (SDM) system. The system contains a material deposition station and a plurality of processing stations (for mask making, heat treating, packaging, complementary material deposition, shot peening, cleaning, shaping, sand-blasting, and inspection). Each processing station performs a separate function such that when the functions are performed in series, a layer of an object is produced and is prepared for the deposition of the next layer. This system requires an article transfer apparatus, a robot arm, to repetitively move the object-supporting platform and any layers formed thereon out of the deposition station into one or more of the processing stations before returning to the deposition station for building the next layer. These additional operations in the processing stations tend to shift the relative position of the object with respect to the object platform. Further, the transfer apparatus may not precisely bring the object to its exact previous position. Hence, the subsequent layer may be deposited on an incorrect spot, thereby compromising part accuracy. The more processing stations that the growing object has to go through, the higher the chances are for the part accuracy to be lost. Such a complex and complicated process necessarily makes the over-all fabrication equipment bulky, heavy, expensive, and difficult to maintain. The equipment also requires attended operation.
In U.S. Pat. No. 4,665,492, issued May 12, 1987, entitled "Computer Automated Manufacturing Process and System" Masters teaches part fabrication by spraying liquid resin drops, a process commonly referred to as Ballistic Particle Modeling (BPM). The BPM process includes heating a supply of thermoplastic resin to above its melting point and pumping the liquid resin to a nozzle, which ejects small liquid droplets from different directions to deposit on a substrate. Commercial BPM machines are capable of jetting only low Tg thermoplastics such as wax, acrylonitrile-butadiene-styrene (ABS), high-impact polystyrene (HIPS), etc. Such a system with a single nozzle and single material supply does not permit fabrication of a multicolor object. BPM process is also further proposed in (1) W. E. Masters, "System and Method for Computer Automated Manufacture with Reduced Object Shape Distortion" U.S. Pat. No. 5,216,616, June 1993, (2) H. E. Menhennett and R. B. Brown, "Apparatus and Methods for Making 3-D Articles Using Bursts of Droplets," U.S. Pat. No. 5,555,176, September 1996, and (3) D. W. Gore, "Method for Producing a Freeform Solid-Phase Object from a Material in the Liquid Phase," U.S. Pat. No. 5,257,657, November 1993. In (3), Gore adapted the BPM technique for deposition of metal droplets. In a series of patents (U.S. Pat. No. 5,617,911, April 1997; U.S. Pat. No. 5,669,433, September 1997; U.S. Pat. No. 5,718,951, February 1998; and U.S. Pat. No. 5,746,844, May 1998.), Sterett, et al. disclosed a method and apparatus for building metal objects by supplying, aligning and depositing nearly uniform metal melt droplets. Metal droplet stream modeling was developed by Orme and Muntz (U.S. Pat. No. 5,340,090, August 1994; U.S. Pat. No. 5,259,593, November 1993; U.S. Pat. No. 5,226,948, July 1993; and U.S. Pat. No. 5,171,360, December 1992.). These metal droplet processes do not lend themselves for the fabrication of multi-color objects.
In U.S. Pat. No. 5,136,515, August 1992, Helinski proposed a RP process for producing a 3-D object layer by layer by jetting droplets of two different hardenable materials into the various layers with one material forming the object itself and the other forming a support for the object as necessary. In two follow-up patents (U.S. Pat. No. 5,506,607, April 1996 and 5,740,051, April 1998), Sanders, et al provided a more detailed description of this inkjet-based process. These three patents led to the development of commercial inkjet printing systems, e.g., Model Maker-II by Sanders Prototypes, Inc. These systems make use of wax and low-melting thermoplastic materials with the object being of one color and the support structure of another color. The process proposed by Yamane, et al. (U.S. Pat. No. 5,059,266, October 1991 and U.S. Pat. No. 5,140,937, August 1992.) involves jetting droplets of a thermosetting material from print-heads to a stage, which is used to mount a 3-D object being built. The print-head unit is positioned below the stage. The jetting direction and jetting amount of the material can be changed according to the geometry information of the object. This process is similar to BPM in that two or more printheads can be used to deposit materials from different orientations. A difference is that the printheads in the Yamane process are generally orientated upside-down so that the droplets are ejected generally upward. Due to no support structure, it is difficult for this upside-down inkjet process to build any object with features such as an overhang, an isolated island or any other non-selfsupporting comer. In addition, the prior-art processes disclosed in the above five patents ('515, '607, '051, '266, and '937) suffer from the following common shortcomings:
(1) Although these patents explicitly suggested or implicitly implied that different colors could be added to a 3-D object by using a plurality of nozzles to dispense materials containing different colors, they failed to fairly suggest how this could be effectively accomplished. Hitherto, this has not been a trivial task. This difficulty can be more easily understood if one recognizes the fact that a typical CAD file carries only geometry information but little or no information on material features such as color. For instance, the defacto standard format used in the RP industry is the .STL file format. As stated earlier, a .STL file is typically composed of a collection of triangular facets each being defined by three vertex points and one normal vector. The file does not contain any message on color. Based on a .STL file and the corresponding data of subsequently sliced layers, a fabrication tool (e.g., a print head) would not know when, where, and how to impart a desired color to a specific location of an intended 3-D object. PA1 (2) Current inkjet printhead-based RP technologies are essentially limited to the fabrication of an object from low-melting thermoplastic materials or wax. These patents failed to suggest any realizable higher melting, higher molecular weight, or higher strength polymers that can effectively carry different dyes. How droplets of generally high-viscosity polymers containing different dyes could be properly mixed to achieve a broad range of colors in a 3-D object remains largely unexplored. PA1 (3) These patents failed to recognize critical differences between traditional 2-D color inkjet printing and 3-D inkjet-based RP processes. For instance, 2-D printing involves ejecting dye-containing water onto a sheet of paper (normally a white color paper). To obtain any color, one simply operates an inkjet printhead to eject different proportions of yellow, cyan (or blue), and magenta (or red). Black spots are usually obtained by ejecting droplets of black ink, rather than by adding the three elemental colors together. The white color area is simply the area on a sheet of white paper where it receives no ink at all. In 3-D color inkjet printing, one would have to use a nozzle to dispense a white color base material or a white colorant-containing material. One no longer has a sheet of white paper for use as the background color. PA1 (a) a droplet deposition device that comprises a multiplicity of flow channels with each channel being supplied with a solidifiable colorant-containing liquid composition. This deposition device further comprises at least one nozzle with each nozzle having, on one end, a fluid passage in fluid flow communication with one of these channels and, on another end, a discharge orifice; PA1 (b) actuator means located in control relation to these channels for activating droplet ejection through the discharge orifice; PA1 (c) a generally flat object-supporting platform in close, working proximity to the discharge orifice to receive liquid droplets therefrom; PA1 (d) motion devices coupled to the platform and the deposition device for moving the deposition device and the platform relative to one another in an X-Y plane defined by first (or X-) direction and a second (or Y-) direction and in a third (or Z-)direction) orthogonal to the X-Y plane to deposit the droplets into a three-dimensional object. The motion devices are controlled by a computer system for positioning the deposition device with respect to the platform in accordance with the CAD-generated data file representing the geometry and color pattern of a desired object. PA1 (1) a droplet dispensing device for providing a bulk of the materials needed to build the object on a layer-by-layer basis. PA1 (2) a 2-D printing device for delivering desired inks to desired locations of the object. This printing device may comprise a majority of the components commonly found in a 2-D inkjet printer, excluding the paper feeding and transporting mechanism. This printer comprises primarily a cartridge that carries four print heads (for yellow, cyan, magenta, and black inks, respectively). The cartridge is driven by a first motion device (e.g., a motor and drive belt) to move horizontally in an X-direction (perpendicular to the paper movement direction in a conventional 2-D color printer). PA1 (3) a computer and supporting software programs operative to create a three-dimensional geometry and color pattern of a desired object, to convert the geometry into a plurality of segments defining the object with each segment coded with a color, and to generate programmed signals corresponding to each of said segments in a predetermined sequence. The data on color pattern is used to drive the 2-D color printer and the data on geometry is used to drive the droplet deposition device and related motion devices; PA1 (4) an object-supporting platform in close, working proximity to the dispensing devices to receive liquid droplets therefrom; PA1 (5) a second motion device (e.g., a 3-D gantry table) coupled to the platform and the droplet dispensing device for moving the dispensing device and the platform relative to one another in an X-Y plane defined by the X and Y directions and in a third or Z direction orthogonal to the X-Y plane to deposit the droplets into a three-dimensional object; and PA1 (6) a three-dimensional machine controller electronically linked to the computer and the first and second motion devices and operative to actuate the motion devices in response to the programmed signals. PA1 (a) providing a computer and supporting software programs operative to create a three-dimensional geometry and a color pattern of a desired object and to convert the geometry and color pattern data into programmed signals in a predetermined sequence; PA1 (b) providing an object-supporting platform with a generally flat surface; PA1 (c) responsive to the programmed signals, operating at least one droplet dispensing device for depositing droplets of a baseline body-building material to build a portion of a first layer of the object onto the flat surface of the platform; PA1 (d) further responsive to the programmed signals, operating a 2-D color printing device for depositing desired color inks onto this portion of this first layer; PA1 (e) repeating (c) and (d) to complete the formation of the first layer; and PA1 (f) repeating (c), (d), and (e) to build multiple layers of the object. Alternatively, step (c) is operated to build a complete layer, upon which color dyes are then deposited to form a complete color pattern on this layer of body-building material by operating step (d).
Because the 2-D color printing technology is relatively well-advanced, it would be advantageous to integrate selected operational procedures and apparatus components for 2-D printing with those for 3-D solid freeform fabrication to constitute a 3-D color model making system.
Therefore, an object of the present invention is to provide a layer-additive process and apparatus for producing a multi-color 3-D object on a layer-by-layer basis.
It is a further object of the invention to provide a computer-controlled process and apparatus for fabricating a colorful 3-D object.
It is another object of the invention to provide a process and apparatus for building a CAD-defined object in which the color pattern can be predetermined.
A specific object of the invention is to integrate 2-D color printing operations with 3-D object building operations to produce multi-color objects.